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Large scale Offshore Wind Farms has emerged as a critical renewable ener-gy technology to reduce GHG (Green House Gas) emission and autonomy in energy production. Each of these wind farms consist of many Wind Turbine Generators (WTG) mounted on a support structure and are capable of gener-ating up to (as we write the paper) 1.2GW of power. These ar...
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... further details Nikitas et al (2016). Figure 11 shows two models: (a) a model of a helicopter as it lands on a sur- face; (b) Wind turbine structure together with the support system. Figure 12 shows an experiment whereby the helicopter collapsed due to resonance type failure. De- pending on the rotational speed of the blades, the helicopter can be set to reso- nance leading to failure. ...
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The purpose of the present study is to review the state-of-the-art in research and development of offshore wind turbines in order to address the latest findings and trends in structural design and response analysis. This could enhance a development of sophisticated offshore wind turbines. To complete such a task, a detailed review of offshore wind...
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... The reasonable performance of these structures both functionally and economically is one of the main concerns in the OWT projects. It needs to be noted that for these giant structures with a design life of 25 years, the design of the foundation which costs about 25-34% cost of the whole project is one of the most costly parts of the whole system [1] . In this regard, the current study concerns the performance of the offshore wind turbine system during environmental loads (cyclic seawave and earthquakes) with a focus on the geotechnical part of the system (foundation and the surrounding soil) which has been less investigated. ...
... , (1) and ́ are deviatoric and and are volumetric components of the plastic strain. Deviatoric plastic strain is defined based on the associative flow rule (́ = ) and ́ can be expressed as ́ which is specified based on the yield surface. ...
The effect of soil-monopile-structure interaction is of great importance in the design of offshore wind turbines (OWTs). Although sea waves play the most effective role in the performance of OWTs, the coupled effect of sea-wave loads and seismic motion on the performance of the OWT system in seismic-prone areas is a factor that is less investigated and should not be ignored. In this regard, a 2-D porous model based on Biot’s poro-elastic theory is considered to capture the pore water pressure generation in the soil domain surrounding the OWT foundation. The coupled effect of sea waves and seismic motion through a comparative study is considered for the reference OWT system based on the monopile foundation by using the FE program, OpenSees. The results of the analyses are presented in specific locations. Upon the obtained results, the dynamic behavior of the OWT system and the possibility of liquefaction in the soil surrounding the OWT during applied loads are investigated and compared. This comparison is a good representative of the effect of the seismic motion on the performance of the OWT system and the soil medium by considering soil-monopile-structure interaction in seismic-prone areas.
... In Fig. 1. Offshore wind turbine foundation/mooring options, in the move from shallow to deeper water (from Bhattacharya et al. (2018)). ...
Marine renewable energy (MRE) is a label that embraces a range of technologies used to harness ocean energy, including wave, tidal stream, tidal barrage, ocean thermal energy conversion (OTEC) and salinity gradient, as well as offshore wind (floating and fixed). For the current analysis, floating solar is omitted from the MRE set. With an increasing drive towards zero-carbon energy provision, and the need for complementarity with increasing penetration of wind and solar, the need to tap the vast available MRE resources has never been greater. Ultimately, the adoption of MRE energy harnessing technology is contingent on the cost of MRE being competitive with other renewable, and conventional, energy sources, in terms of Levelised Cost of Energy (LCoE). The value of appropriate control systems, which can maximise the energy conversion capability of MRE and give added value to the capital investment, has been identified as an important modulator of LCoE. This paper examines the range of control problems within the gamut of MRE technologies and documents commonality and contrasts, as well as the emergence of control problems that are unique to aspects of MRE
... For Phase 3, maintenance, energy consumption of two boats (i.e., six trips per year of the transfer boat for small maintenance operations and one trip per year of the fast supply vessel with replacement components) and of a helicopter (one trip per year) for monitoring the farms, are considered in line with Weinzettel et al. (2009), Tsai et al. (2016 and Wang S. et al., 2019. Replacement of worn parts mostly concern factory preassembled technological components, such as the gearbox, which are transported to the site (in line with Bhattacharya et al., 2018;Chipindula et al., 2018;Wang S. et al., 2019). ...
Floating wind turbines are a valid option for offshore wind farms in the Mediterranean, where the sea-floor falls off rapidly with distance from the coastline. The present study concerns a Life Cycle Assessment of the environmental performance of two types of floating wind turbine. Greenhouse gas emissions of two standard models (raft-buoy and spar-buoy, 154 m rotor diameter, 6 MW installed power) were estimated in terms of Global Warming Potential (t CO2eq) with the aim of determining a benchmark for evaluating the performance of similar offshore wind farms. Thus, the aim of the paper was to create a benchmark for the design of innovative technologies, such as those developed by specialist companies, and to verify the validity of new designs and technologies in terms of avoided greenhouse gas emissions. The results show that the Carbon Intensity of Electricity of a single floating wind turbine varies in the range 26–79 g CO2eq·kWh−1, averaging 49 g CO2eq·kWh−1, in line with other studies of offshore wind turbines and other renewable energy sources (such as onshore wind and photovoltaic). Extension of our study to the whole life cycle, including manufacturing, assembly and installation, maintenance and material replacement and a hypothetical decommissioning and end-of-life, showed that wind farms are among the most promising marine renewable energy technologies for the Mediterranean.
... The natural frequency of the reference OWT system is 0.25 Hz located in the soft-stiff range soil layers as it is recommended by DNVGL to avoid resonance problems. Based on Bhattacharya, Nikitas, and Jalbi (2018), the qualitative power spectrum of main forcing frequencies for an NREL 5 MW wind turbine indicates a lowfrequency range for wind loads in comparison to the sea-wave loads that are much closer to the natural frequency of the OWT system. Thus, it appears more meaningful to consider the sea-wave loading to be more significant. ...
Prediction of the dynamic performance of an offshore wind turbine (OWT) requires consideration of many different design parameters. Besides the superstructure, the OWT foundation also plays an important role both functionally and financially in the design. In this study, numerical dynamic analyses of an offshore wind turbine with a monopile foundation are performed under wave loading that may lead to soil liquefaction around the pile due to cyclic stresses induced by the pile displacements using the open-source program, OpenSees. Effects of foundation properties such as monopile diameter, pile embedment depth, and sea-wave characteristics such as its period, sea-water depth, duration, and level of the loading on the dynamic performance of the system are investigated. The results in terms of deformations, excess pore water pressure, and inertial forces are presented and discussed. The findings are considered as valuable guidance on the estimation of the dynamic performance and liquefaction susceptibility of the offshore wind turbine foundations under cyclic sea-wave loads.
Simplified design procedures for offshore wind turbine (OWT) support structures are necessary in the concept and tender design stages for assessing the financial viability. Building upon the previous research on simplified monopile design, this paper presents a similar method to design jacket supported OWTs founded on piles or suction caissons. The method is based on the minimum and necessary data, namely the site characteristics (wind speed at reference height, wind turbulence intensity, water depth, wave height and wave period), turbine characteristics (rated power, rated wind speed, rotor diameter, cut-in and cut-out speed, mass of the rotor-nacelle-assembly) and ground profile (soil stiffness variation with depth and soil strength). A flowchart of the design process is also presented for visualisation of the rather complex multi-disciplinary analysis. Insights are given for 3 and 4 legged jackets. The calculation procedures that are required can be easily carried out either through a series of spreadsheets or simple hand calculations. An example problem emulating the design of a jacket on piles is taken from literature to demonstrate the proposed calculation procedure. The data used for the calculations are obtained from publicly available sources and the example shows that the simplified method arrives at a similar foundation to the one reported.
Offshore wind turbines (OWTs) have emerged as a reliable source of renewable energy, witnessing massive deployment across the world. While there is a wide range of support foundations for these structures, the monopile and jacket are most utilized so far; their deployment is largely informed by water depths and turbine ratings. However, the recommended water depth ranges are often violated, leading to cross-deployment of the two foundation types. This study first investigates the dynamic implication of this practice to incorporate the findings into future analysis and design of these structures. Detailed finite element (FE) models of Monopile and Jacket supported OWTs are developed in the commercial software, ANSYS. Nonlinear soil springs are used to simulate the soil-structure interactions (SSI) and the group effects of the jacket piles are considered by using the relevant modification factors. Modal analyzes of the fixed and flexible-base cases are carried out, and natural frequencies are chosen as the comparison parameters throughout the study. Second, this study constructs a few-parameters SSI model for the two FE models developed above, which aims to use fewer variables in the FE model updating process without compromising its simulation quality. Maximum lateral soil resistance and soil depths are related using polynomial equations, this replaces the standard nonlinear soil spring model. The numerical results show that for the same turbine rating and total height, jacket supported OWTs generally have higher first-order natural frequencies than the monopile supported OWTs, while the reverse is true for the second-order vibration modes, for both fixed and flexible foundations. This contributes to future design considerations of OWTs. On the other hand, with only two parameters, the proposed SSI model has achieved the same accuracy as that using the standard model with seven parameters. It has the potential to become a new SSI model, especially for the identification of soil properties through the model updating process.
